1. Field of the Invention
The present invention relates to a method for producing a chlorosilane gas, and more specifically to a method for producing trichlorosilane using tetrachlorosilane in a more efficient manner.
2. Description of the Related Art
Trichlorosilane (SiHCl3, TCS) is a compound useful as a raw material for highly pure polycrystalline silicon, also called polysilicon. Trichlorosilane reacts with hydrogen at a temperature as high as at least 1000° C. to deposit polysilicon. The reactions for the deposition of polysilicon are typically represented as follows:4SiHCl3→Si+3SiCl4+2H2  (1)SiHCl3+H2→Si+3HCl  (2)
Trichlorosilane used in the reactions for the deposition of polysilicon is generally produced by reacting metal silicon with hydrogen chloride. For example, a method for producing trichlorosilane using a fluidized-bed reactor is disclosed in which metal silicon reacts with hydrogen chloride in the presence of a catalyst containing iron and aluminum, as depicted in Reaction 3:Si+3HCl→SiHCl3+H2  (3)
As a result of the reaction, gaseous products are obtained. Thereafter, the gaseous products are condensed by cooling to −10° C. or less. However, this condensate includes other chlorosilanes as by-products as well as trichlorosilane. The trichlorosilane is separated and collected from the condensate by distillation and is then used as a raw material for the production of polysilicon. Tetrachlorosilane (SiCl4, STC) is also separated by distillation. The tetrachlorosilane is converted to trichlorosilane (TCS), typically by Reaction 4:3SiCl4+2H2+Si→4SiHCl3  (4)
The trichlorosilane is reused for the production of polysilicon.
Another method for producing trichlorosilane was proposed (see FIG. 1). According to this method, metal silicon particles having a size of about 100 to about 300 μm, hydrogen chloride, tetrachlorosilane, and hydrogen are fed into a fluidized-bed reactor filled with metal silicon particles, and the reaction of the metal silicon and the hydrogen chloride (Reaction 3) and the reaction of the metal silicon, the tetrachlorosilane, and the hydrogen (Reaction 4) are allowed to proceed simultaneously in the reactor to produce trichlorosilane. As the reactions proceed, the metal silicon particles are gradually reduced in size, which requires the replenishment of fresh metal silicon particles. Since a change in the temperature of the raw materials is monitored to determine when to replenish the fresh metal silicon particles, the reaction temperature is not constant and fluctuates, and as a result, the quality of the product becomes non-uniform depending on the reaction time.